The United States and Japan will step up their defence cooperation to deal with the threat from nuclear-armed North Korea as tensions in East Asia remain high, officials from the two allies said on Thursday.

Pearce guilty of 'poor judgment':Coalition

NSW Attorney-General Greg Smith has defended his former cabinet colleague Greg Pearce, telling reporters there's a world of difference between the former finance minister's lapse in judgment and straight-out corruption.

Mr Pearce was sacked by Premier Barry O'Farrell on Thursday for failing to disclose a conflict of interest when appointing his wife's boss to the board of Sydney Water in 2011.

Mr Smith said that Mr Pearce's transgression shouldn't be compared to the alleged behaviour of Eddie Obeid and Ian Macdonald, two former Labor ministers who were this week found to have acted corruptly by the Independent Commission Against Corruption (ICAC).

"I think there's quite a deal of difference between corrupt conduct and, say, poor judgment, which seems to be the issue with my ... former colleague," Mr Smith said on Friday.

He said his coalition colleagues tried to ensure they were above reproach.

"Naturally we all are watching and keeping close watch to make sure that we act responsibly and act honestly," he said.

NSW Labor leader John Robertson says he wants a full investigation into other board appointments made by Mr Pearce during his two years as a minister, as well as allegations Mr Pearce took taxpayer-funded weekends away.

"That's why I wrote to the head of Premier and Cabinet (Chris Eccles) last night and said I want to see all documents seized and secured so that we don't see that sort of information being destroyed," Mr Robertson told reporters on Friday.

He's asked Mr Eccles to keep records of any documents that are destroyed.

Between the sacking and the corruption findings, Mr Robertson said it had been a "terrible week" for both sides of politics.

Mr Pearce's replacements were sworn in by Governor Marie Bashir at a ceremony at government house.

Former disability services minister Andrew Constance has taken the finance portfolio, while upper house MP John Ajaka has been promoted to cabinet to take Mr Constance's old ministerial responsibilities and Mr Pearce's Illawarra portfolio.